1. Field of the Invention
The present invention relates to a clock spring in which a flexible cable is utilized to make an electrical connection between a fixed member and a movable member. More particularly, it relates to a type of clock spring in which the fixed member is composed of a stationary housing and a cover that are formed integrally with each other, and the movable member or rotor is rotatably attached to the stationary housing and the cover.
2. Description of the Related Art
FIG. 5 is a cross-sectional view showing a conventional clock spring. In the drawing, numeral 1 denotes a rotor equipped with a disk-like top plate 2 and a cylindrical inner ring wall 3 which is vertically provided at the center of the top plate 2. An indentation 4 is formed at the outer periphery of the top plate 2. Numeral 5 denotes a stationary housing provided with a cylindrical outer ring wall 6 and a brim 7 projecting inwardly from the upper end of the outer ring wall 6. The brim 7 and the indentation 4 of the top plate 2 overlap each other. Numeral 8 denotes a disk-like cover secured to the lower end of the outer ring wall 6 by means of an appropriate fixing method, such as heat caulking or rivets. The cover 8 closes a cable accommodating portion 9 defined between the rotor 1 and the stationary housing 5. The rotor 1, the stationary housing 5 and the cover 8 all form the shell of the clock spring. The rotor 1, which is a movable member, is rotatably coupled to the stationary housing 5 and the cover 8, which constitute a fixed member. Numeral 10 denotes a flat cable made of a plurality of conductors that are laminated by a pair of resin films. It is contained in the cable accommodating portion 9 while the flat cable 10 is coiled a plurality of turns. The ends of the flat cable 10 on the inner and outer peripheries thereof are respectively secured to the rotor 1 and the stationary housing 5, and are then led outside.
The rotor 1 is secured to the side of the steering wheel of the steering system of an automobile, whereas the stationary housing 5 and the cover 8 are secured to the fixing side of the body of the automobile. In such a state, the clock spring constructed as described above is employed. When the turning force of the steering wheel rotates the rotor either clockwise or counterclockwise, the flat cable 10 is either wound around the inner ring wall 3 of the rotor 1 or rewound around the outer ring wall 6 of the stationary housing 5. In either case, an electric connection between the movable member (rotor 1) and the fixed member (stationary housing 5 and cover 8) is made through the flat cable 10.
Because of the construction of the conventional clock spring in which the movable member or rotor 1 is rotatably attached to the fixed member, composed of the stationary housing 5 and the cover 8, a clearance (space indicated by S in FIG. 5) must be formed in the portion where the movable and fixed members are joined together, that is, between the outer circumference of the top plate 2 of the rotor 1 and the internal peripheral surface of the outer ring wall 6 of the stationary housing 5. The clearance S formed between the rotor and the stationary housing serves to absorb any dimensional and mounting errors of the parts of the clock spring. However, because of this clearance while the flat cable 10 is being wound or rewound, if vibration is applied to the clock spring from the outside, the extreme end of the flat cable 10 on the outer periphery thereof enters the clearance S. The upper and lower ends of the flat cable 10 along its width direction strike against the brim 4 or the cover 8, thus producing unpleasant noise.